Nematodes, commonly referred to as "roundworms", comprise a phylum of about 12,000 species of unsegmented terrestrial, freshwater, or marine worms. Both saprophytic and parasitic forms are known. Parasitic nematodes are recognized as having either needle or odonto (tooth-like) stylets. Nematodes are abundant in the surface layers of soils and are found throughout the world. They are recognized by having cylindrical, tapering, simple bodies that comprise an interior gut and a muscular outer wall that are separated by a fluid-filled cavity. Nematodes range in size from microscopic to about 10 cm (about 4 in) long. A few species are hermaphroditic, but most have separate sexes.
Nematodes have raised great economic and humanitarian concern due to their impact on the world's agricultural output as well as their impact on human and animal suffering and disease. Regarding the impact nematodes have on agriculture, annual world-wide losses resulting from nematode infestation have been estimated to be about $78 billion. In the United States alone, annual losses due to nematode-related crop diseases are estimated to be about $8 billion. The impact on a crop production by a single nematode-related pathogen can be severe. For example, the soybean cyst nematode causes annual losses of about $267 million in the north central United States; $38 million in state of Missouri alone.
Tomatoes and strawberry production are often the agronomic crops most severely impacted by nematode infestation. Control of nematode infestation of these crops historically has depended on low cost, highly effective chemicals including methyl bromide (CH.sub.3 Br), ethylene dibromide (C.sub.2 H.sub.4 Br.sub.2, "EDB"), and 1,2-dibromo-3-chloropropane (C.sub.3 H.sub.5 Br.sub.2 Cl, "DBCP"). However, the application of these workhorse pesticides has been or will soon be banned by governmental regulatory agencies for their unwanted health and environmental impacts. The resulting economic impacts from these bans will be severe. The National Pesticide Impact Assessment Program ("NAPIAP") has estimated annual economic losses of $1.3 to $1.5 billion in the United States from a ban on the agricultural use of methyl bromide. In California, for example, the Office of Pesticide Consultation and Analysis of the California Department of Food and Agriculture estimated in 1996 that economic damages resulting from a ban on using methyl bromide will result in crop losses totaling between about $287 and $346 million, in addition to $241 million in trade income. Estimates of more than $500 million in crop losses are projected for Florida See Spreen, T. H., et al., Bull. Univ. Fla. Exp. Stn. No. 898 (1995).
Unfortunately, no truly viable successor to methyl bromide, EDB, or DBCP has been found. The pesticides sold commercially under the tradenames Temik and Dazomet have limited registration. Other commercially available pesticides, such as those sold under the tradenames Carbofaran, Vapam, and Chloropicrin, have limited effectiveness. Still other nematicides have been shown to be carcinogenic (e.g., the pesticide sold as Telone). Recently the pesticides sold under the names Aldicarb and Carbofuran have lost registration. Development of new chemicals having effective nematicidal applications in the near future appears remote; in fact, no new nematicide has been developed since 1974.
Non-pesticide alternatives to nematode control have been disappointing. Pre-plant fumigation alternatives do not provide the same level of nematicidal effectiveness as methyl bromide. Several fungal parasites of nematodes have been reported, but none of these has been developed into a commercial product. Morgan-Jones and Rodriguez-Kabana, Vistas on Nematology Ch. 14, 1987; Kerry, Biological Control in Crop Production Ch. 5 (1981). In particular, the use of these fungi for nematode control has not resulted in significant improvement of plant growth. See, e.g., Townshend, et al., 21 J. Nematology 179-183 (1989). This failure is probably inherent from the mechanisms used by fungi to kill nematodes. Many of these fungi rely on the migration of the nematode into a trapping structure present in the fungus. Thus, the effectiveness of the fungus' nematicidal activity depends critically on the relatively random occurrence of two different organisms coming in proximity of each other. Such a mechanism of nematicidal action has little effect on endoparasitic or sedentary nematodes.
Nematodes also cause human and animal suffering and/or death. Medically significant forms of nematode include the various genera known as hookworm, the filaria of which cause elephantiasis; and the trichina worm, the cause of trichinosis. Heartworm and pinworm are still other nematode species that cause debilitating disease and death, especially in animals such as dogs, cats, horses, and cattle. In food animals, e.g., pigs and cattle, nematode (worm) infection significantly reduces meat/dairy production efficiency since the infected producing animal requires greater quantities of feed to produce the same amount of food as an uninfected animal. Generally, ivermectin is the leading treatment for worm infection in horses and cattle. However, ivermectin is expensive.
Thus, a serious need exists for new and effective compositions and strategies to control nematode infestation. The present invention meets these and other important needs.